Surface weathering and erosion as a result of environmental exposure is a key area of research for any corporation, research facility or government entity that purchases or produces products that can corrode as a result of that exposure to the environment. If the impact of environmental exposure can be significantly decreased from the initial production of the product and throughout its useful lifetime, it will lower the total cost of ownership for the corporation, research facility or government entity.
Sprayable organic corrosion preventative or protective compounds (CPCs) that penetrate crevices and faying surfaces and leave a flexible, waxy, waterdisplacing layer have extended the time between corrosion rework, thereby lowering the impact of environmental exposure. Experiments in the field have shown that CPCs release only marginally effective corrosion inhibitors, as compared to the release of inhibitors provided by primers and conversion coatings. CPCs primarily act to displace and repel water without any significant chemical reaction with the corrosive or potentially corrosive elements.
Aluminum alloy corrosion inhibitors, such as chromate, inhibit corrosion by slowing the rate of the oxygen reduction reaction (ORR) at local cathodes on the alloy surface (W. J. Clarke and R. L. McCreery, J. Electrochem. Soc., 149, B379 (2002) and W. J. Clarke, J. D. Ramsey, R. L. McCreery, G. S. Frankel, J. Electrochem. Soc., 149,B 179 (2002)). As schematically shown in Prior Art FIG. 1, the copper (Cu) rich intermetallics in high strength aluminum alloys 110 form active cathodes at the intermetallics or through dissolution and redeposition of Cu 120 to adjacent surfaces 100 (R. G. Buchheit, M. A. Martinez, L. P. Montes, J. Electrochem. Soc., 146(12), 4424 (1999)).
U.S. Pat. 4,226,624 issued to Ohr (Oct. 7, 1980) addresses the issue of corrosion of metallic structures. Specifically, Ohr found that utilizing inorganic salts—such as chromates—will reduce the incidence of corrosion in these metallic structures. The problem with the use of inorganic salts is that they don't dissolve in organic materials such as paints or plastics. Therefore, modifying the structure of the inorganic salts to include organic substituents may make them more soluble in these coatings and materials. Ohr utilizes organo-substituted quarternary ammonium salts in order to facilitate the incorporation of these compounds into organic materials. The inorganic salts must be substituted with organic moieties in order to make them soluble in other organic materials. One consideration in this approach is that chromates can pose an unacceptable environmental risk.
Based on the drawbacks, disadvantages and cost issues of environmental exposure for corrodible surfaces and products, it would be useful to develop and implement active corrosion inhibitors and compositions/materials that contain those inhibitors that a) are incorporatable into coatings, paints and other products utilized in protecting corrodible materials; b) are compatible with conventional corrosion inhibitor compounds (CICs) or corrosion protective compounds (CPCs); c) react with structural surfaces to slow corrosion; d) can transport or facilitate transportation of corrosion inhibitors to the corrosion site “on demand” as triggered by the presence of corrosive conditions; and e) is an acceptable additive with respect to not posing unnecessary environmental risks. If these types of compositions that contain both an active corrosion inhibitor and a conventional CIC or CPC can be developed, they could extend what is currently considered the useful life of conventional CICs or CPCs in products that incorporate corrodible surfaces.